The present invention relates to an automatic selector device of a change-speed gearbox of a motor vehicle with a frictional connection (i.e., a clutch or brake) which can be engaged by a selector setting element, a selector valve for subjecting the selector setting element to working pressure and a gear retention control valve connected to the selector setting element and to the selector valve.
DE-AS 22 12 679 shows a hydraulic selector device for power shift gearboxes having gear selector valves connected to a pressure conduit and movable into selector position by electromagnetically actuated pilot control valves. Each of the gear selector valves controls a conduit connection between the pressure conduit and a gear clutch, and has a device in the gear selector valves by way of which, on gear change, the engagement or disengagement of the clutches is controlled with overlap. Each gear selector valve contains, on the same axis, a selector spool with two spool parts with two spool surfaces of different sizes together with a control spool and a plurality of shut-off spools. The spool part with the smaller spool surface faces towards the control spool, and the shut-off spools connect to the other spool part. The pressure conduit for connecting the spool part with the larger spool surface to the ventilation hole is released by the other spool part; each clutch is connected to a selector spool of its associated gear selector valve and to a shut-off spool of each of the other gear selector valves.
In this known selector device, an effort is made to avoid incorrect gear selections so that, should defects appear in the electrical part of the selector device, it is impossible for two gears to be engaged simultaneously. For this purpose, the arrangement in the known selector device is such that intermediate valves are located between the pilot control valves and the gear selector valves. These intermediate valves are connected to the pilot control valves by the control conduits. Furthermore, the intermediate valves are connected in series in a bypass conduit of the pressure conduit, with the intermediate valves each controlling one of the bypass conduits which can be connected to the gear selector valves as a function of the pilot control valves which can be actuated individually or in combination.
An electrohydraulic control system for controlling a plurality of hydraulic load devices is shown AT E 23 213 B. This system has a plurality of multi-position control valves, (in fact, one for each load device) in order to control the flow of fluid to and the removal of fluid from the load devices. Each control valve has first and second hydraulic servo-devices in order to move the control valve into its respective first and second positions. In addition, the system includes a plurality of pilot control valves actuated by an electromagnetic winding (one winding for each control valve). It is possible to actuate each pilot control valve in order to supply fluid to the corresponding servo-device and to move the corresponding control valve into one of its two end positions.
The objective of this known control system is to improve an electrohydraulic control system which uses a minimum number of valves actuated by electromagnetic windings and is reliable in its mode of operation. For this purpose, the known control system provides for the control valves to be two-position valves, for the pilot control valves actuated by electromagnetic winding to supply fluid to corresponding first servo-devices in order to move their associated control valves into a first position and, by way of a reset valve, which can be actuated by an electromagnetic winding. The reset valve is common to the control valves and can be actuated in order to supply fluid to the second servo-devices in order to move each control valve into its second position. In this manner, the necessary number of valves actuated by electromagnetic winding is only greater than the number of load devices by one number.
In another known selector device shown in ATZ 88, No. 12, page 681 (1986), division into an electronic part and a hydraulic part is provided. Whereas the hydraulics are responsible, inter alia, for subjecting the respectively actuated selector setting elements to pressure, the electronics control the gear change and also, to some extent, the level of the hydraulic pressure.
The connection between the electronics and the hydraulics is generally effected by electromagnetic 3/2-way valves. These are configured such that, when they are excited (i.e. when an electric current flows through their coil), the associated selector setting element is subjected to hydraulic pressure. Interruption of the flow of current to the solenoid valves, whether or not this is due to a defect in the electronic control or failure of the voltage supply, leads to interruption of the force path. This can lead to dangerous driving situations either because, in overrun, the engine brake (and possibly a retarder located in front of the gearbox) become ineffective or, when the engine is providing traction, the engine torque is no longer available on a gradient.
In order to avoid the above-mentioned problem for example, so-called locking solenoid valves can be used. These locking solenoid valves are equipped with a permanent magnet which ensures that in the absence of a supply of current, the solenoid valve remains in a position once it has been reached. Switching over into the respective other position takes place by way of a short selector pulse whose sign defines the position selected.
A disadvantage of this solution, apart from the relatively complicated design of the electromagnetic valve and the triggering necessary using a reversible current direction, is that the valve position selected is not unambiguously defined when there is no current flowing through the coil. Thus it could happen, for example, that a valve previously located in the activated position could move unintentionally into the deactivated position due to vibration, external magnetic fields, etc. This would again deprive the respective selector setting element of pressure.
Even more serious in such a solution would be the problem of defined deactivation. If the electrical connection to a solenoid valve should be interrupted, the latter and therefore the associated selector setting element could no longer be deactivated so that, for example, it would be more difficult to tow the vehicle, or the gearbox could even be jammed if a different frictional connection (clutch or brake) were deactivated.
In the selector device according to the above-mentioned patent application Ser. No. 07/914,536, with the same priority, these disadvantages are avoided. A gear retention control valve is used which can be moved into its gear retention position by spring force and into its gear release position by an electromagnet. With a plurality of selector setting elements, such a gear retention control valve can only be associated with one selector setting element in each case, and the number of selector setting elements then is equal to the number of gear retention control valves. A common gear retention control valve can be used for either a plurality of or all of the selector setting elements.
In all instances with the selector device according to the related patent application, the gear retention control valve can be used for those selector devices in which a common pressure control valve controls the working pressure for a plurality of selector setting elements and an electromagnetic 3/2-way control valve is respectively used both for the selector valve and for the control valve. The gear retention control valve can also be applied in a corresponding manner to those selector devices in which the working pressure for each selector setting element is separately controlled. For this purpose, a pressure control valve is respectively used both for the selector valve and for the control valve.
The gear retention control valve is switched over first in the case of a failure of the electronics so that the section of the control pressure conduit connected to the selector valve is connected to the working pressure conduit of the relevant selector setting element. If, on one hand, the control pressure conduit, and therefore also the working pressure conduit, were previously unpressurized, the selector setting element also remains deactivated. If, on the other hand, the working pressure of the selector setting element is above a certain pressure level, the selector valve is held in its correspondingly open position by the working pressure. The selector setting element, therefore, remains activated. The gear retention control valve is, however, itself electromagnetically actuated so that it requires both special triggering by the electronic control unit and a special functional configuration of this control unit.
An object of the present invention is to keep the control requirements for the gear retention control valve small in a selector device described in the related patent application.
This object has been achieved in an advantageous manner according to the present invention by providing an automatic selector device of a motor vehicle change-speed gearbox with a frictional connection, a selector setting element for engaging the frictional connection, and a selector valve which has at least one gear position which subjects the selector setting element to working pressure and one zero position which switches off the working pressure from the selector setting element. A spring force moves the selector valve into the zero position, and a pressure surface acts in opposition to the spring force and can be subjected to a control pressure to move the selector valve into a gear position. An electromagnetic control valve whose excitation is influenced by an electronic control unit adjusts the control pressure in proportion to the excitation to move the selector valve into a gear position. A control pressure conduit connects the selector valve to the control valve.
A gear retention control valve is located in the control pressure conduit and has a gear release position and a gear retention position. A spring force moves the gear retention control valve into the gear retention position. An auxiliary control force, which is derived from a magnetic force of the control valve resulting from a permanent minimum excitation, is used to move the gear retention control valve into the gear release position. A conduit section of the control pressure conduit connects the selector valve to the gear retention control valve. In the gear release position, the conduit section is connected to the control valve and is shut off from the selector setting element. In the gear retention position, the conduit section is connected to the selector setting element and is shut off from the control valve. The pressure surface of the selector valve is dimensioned such that the pressure force which results from the control pressure generated by the minimum excitation is smaller than the spring force for moving the selector valve into the zero position.
In the selector device according to the present invention, neither special triggering of the gear retention control valve by the electronic control unit nor a special functional configuration of this unit is necessary. This is because the gear retention control valve is moved into its gear release position by, for example, the control pressure resulting from a permanent minimum excitation of the control valve and, on the occurrence of a fault in the control unit (in which case, the minimum excitation of the control valve also fails as a side effect), is moved into its gear retention position by spring force. The selector valve pressure surface subject to the control pressure is dimensioned such that the minimum excitation is not sufficient to generate a control pressure force which overcomes the spring force for moving the selector valve into the zero position.
Whereas a special pressure medium setting element is additionally required in the case of a pressure actuation of the gear retention control valve, the present invention allows an actuation of the gear retention control valve derived mechanically from the magnetic force of the control valve, and no special setting element is necessary for this actuation. To this end, a structural and functional combination of the control valve and the gear retention control valve is provided.
If a pressure control valve is used for the selector valve, the valve can have a pressure surface configured for feedback of the controlled working pressure. The surface determines the position assumed by the selector valve in the event of a malfunction during which the gear retention control valve is actuated into its gear retention position.